Internal combustion engines are well known and widely used for all manner of applications where production of rotational power is desired. The general principals relating to delivery of a combustible fuel into a cylinder will be familiar to many, with ignition and combustion of the fuel producing a rapid pressure and temperature rise to drive a piston coupled with a rotatable crankshaft. Virtually innumerable variations on the basic strategy of fuel delivery and combustion to drive a piston have been proposed over the years. Engineers have experimented for well over a century with different ways to open and close engine valves, directly or indirectly inject or otherwise deliver fuel, handle exhaust gases, compress intake gases, and a host of other variables. The types of fuel used to power internal combustion engines are diverse as well.
Traditional gasoline engines utilize petroleum distillates that are injected either directly into an engine cylinder, or into an intake conduit feeding air and the fuel to an engine cylinder. Such engines typically employ a spark to ignite a mixture of fuel and air within the cylinder. Diesel engines operate somewhat differently, with fuel injection almost universally occurring directly into the cylinder, and reliance upon high pressure within the cylinder to induce autoignition of fuel and air therein. Traditional gasoline engines and traditional diesel engines offer various advantages in certain applications, and of course certain disadvantages unique to the respective technologies. In recent years, considerations as to exhaust emissions, cost, and resource availability have driven increased interest in so-called gaseous fuel engines.
Gaseous fuel engines typically employ a fuel in gaseous form, such as methane, ethane, propane, and mixtures of these and other hydrocarbon and non-hydrocarbon fuels. Gaseous fuels can be burned in at least certain applications to produce reduced particulate matter and nitrogen oxides, collectively “NOx”, and with better balance between and among certain emissions, as well as potentially greater efficiency in at least certain applications. A challenge in many gaseous fuel engines relates to a relatively greater difficulty in achieving ignition, either because such engines are operated at relatively lean conditions or because constituents of the gaseous fuel are inherently more difficult to ignite.
Engineers have experimented with gaseous fuel ignition in a variety of ways, and in certain engines employ a so-called pre-chamber ignition device. A pre-chamber ignition device can produce a local combustion of a relatively rich mixture of a fuel and air, to produce jets of flame that are directed into a combustion chamber in the engine to ignite a main charge of gaseous fuel therein. The relatively small fuel charge ignited in the pre-chamber may be a liquid fuel, with such engines sometimes being referred to as dual-fuel engines. Other dual-fuel engine strategies rely upon injection of a pilot charge of liquid fuel directly into an engine to ignite a main charge of gaseous fuel. European Patent Application EP3061951A1 is entitled Fuel Injection Unit, and proposes an apparatus for injecting a liquid pilot fuel into a combustion chamber, and also injecting a gaseous medium. Still other strategies have proposed the use of the same fuel for both pilot and main charge functions, utilizing relatively complex and expensive apparatus. No single gaseous fuel ignition technology has yet emerged that shows sufficient promise for widespread commercial adoption, thus there is ample room for improvement in the gaseous fuel engine art.